6/8 



NA TURE 



[October 29, 190S 



(imo of perihelion 3-646 days, and this reduces the mean 

 diurnal motion by o"-38. As M. Bossert found that, in 

 order to represent the 1891 observations correctly, he had 

 also 10 diminish this factor by the same amount, it is 

 suggested that this comet is subject to a negative accelera- 

 lion, such as was found by M. Schulhof for the Tempel, 

 comet, and by M. Lamp for Brorsen's comet. 



In the ephemeris, which covers the period October 20 

 to December 31, the actual positions for i2h. (Paris 

 M.T.) are given for each day, and observations made on 

 September 29 and October 7 show that the ephemeris was 

 correct for R.A. but required corrections in declination 

 of +i''7 and +i''8 respectively. During the period 

 November 1 to December 31 this comet will, according to 

 the ephemeris, apparently travel through the constellations 

 Cancer and Leo, from o = 8h. 45-im., B=+24° 34''9, to 

 a = 9h. 22-7m., 6= + 14° 8'-4 i^AsUonomische Naclirichlcii, 

 No. 4277, p. 79). 



Ephemeris for Jupiter's Eighth S.^tellite. — An 

 ephemeris showing the position of J viii. in regard to 

 Jupiter has been computed bv Messrs. Crawford and Etal. 

 and is published in Circular No. 105 from the Kiel Cenlral- 

 stelle. The following is part of it, and gives the differ- 

 ences : — 



/ -c'ii/: - I for 12//. G.M. T. 



Aa a5 



11 ^ ... 



Oct. 27 ... -2 44-8 ... 426 56 



31 ... -3 3-; ... 4-27 14 

 Nov. 4 ... -3 21 '9 ... + 27 2S 



Saturn's Rings. — Further particulars of the new dark 

 ring surrounding the bright rings of Saturn are published 

 in a message from Herr Schaer, of the Geneva Observa- 

 tory, to No. 4277 of the Asironomische Nachrichten (p. 81, 

 October 20). On October 8 the white ring was seen to 

 be bordered by two narrow bands of a brownish hue. 

 When the seeing was good both bands were seen beyond 

 the edge of the planet's sphere, and from these observa- 

 tions M. Schaer concludes that there is a dark exterior 

 ring somewhat similar to the interior crape ring. This 

 new feature is diflicult to see with the Cassegrain tele- 

 scope of 40 cm. aperture, using powers of 270, 450, and 

 660. 



Prof. Stromgrcn, observing Saturn at Copenhagen on 

 October 10. was unable to see any extraordinarv feature, 

 nor could Prof. Hartwig, at Bamberg on October 10 and 

 II, confirm M. Schaer's observation. Similarly, Senor J. 

 Comas Sola, who observed the planet under good con- 

 ditions during the beginning of the month, states that he 

 saw nothing abnormal. 



INTERNATIONAL CONFERENCE ON ELEC- 

 TRICAL UNITS AND STANDARDS. 

 T NTERN.VTIOXAL agreement on the subject of electrical 

 ■*■ units was arrived at in Paris at the conferences of 

 1881 and 1884, and at Chicago in 1893. The results of 

 these conferences have been of considerable value to elec- 

 trical industries. In recent years, however, differences 

 have occurred, partly in the definitions of the units and 

 partly in their realisation, and the degree of precision in 

 electrical measurements which is now possible rendered it 

 necessary to remove these differences. The committee of 

 delegates at the International Congress at St. Louis in 

 1905 expressed the desirability of summoning an Inter- 

 national Conference on Electrical Units and Standards, 

 and the British Government recentlv invited representatives 

 from all the civilised countries of the world to discuss these 

 subjects. 



The conference was opened by the Right Hon. Winston 

 S. Churchill, M.P., on Monday,' October 12, at the rooms 

 of the Royal Society. Delegates from twentv-four different 

 countries, including Australia, Canada, and India, were 

 then present. Mr. Churchill gave, as one of the main 

 objects of the gathering, the establishment of a universal 

 system of electrical standards acceptable to all. 



Lord Rayleigh was elected president of the conference, 

 and Dr. Glazebrook chairman of a technical committee, 

 Ihe members of which were nominated by the delegates. 



Possibly the best general view of the results of the con- 



ference can be given by the reproduction of the first por- 

 tion of Schedule B containing the resolutions which the 

 conference adopted with the request that the delegates 

 would lay these and the specifications which complete the 

 schedule before their respective Governments with the view 

 of obtaining uniformity in the legislation with regard to 

 electric units. 



Resolutions. 



(i) The conference agrees that as heretofore the magni- 

 tudes of the fundamental electric units shall be deter- 

 mined on the electromagnetic system of measurement with 

 reference to the centimetre as the unit of length, the gram 

 as the unit of mass, and the second as the unit of time. 



These fundamental units are (1) the ohm, the unit of 

 electric resistance which has the value of 1,000,000,000 in 

 terms of the centimetre and second ; (2) the ampere, the 

 unit of electric current which has the value of one-tenlh 

 (o-i) in terms of the centimetre, gram, and second ; (3) the 

 volt, the unit of electromotive force which has the value 

 100,000,000 in terms of the centimetre, the gram, and the j 

 second ; (4) the watt, the unit of power which has the 

 value 10,000,000 in terms of the centimetre, the gram, and 

 the second. 



(2) As a system of units representing the above and 

 sufiicienllv near to them to be adopted for the purpose of 

 electrical measurements and as a basis for legislation, tlie 

 conference recommends the adoption of the international 

 ohm, the international ampere, and the international voll 

 defined according to the following definitions. 



(3) The ohm is the first primary unit. 



(4) The international ohm is defined as the resistance 

 of a specified column of mercury. 



(5) The international ohm is the resistance offered to an 

 unvarying electric current by a column of mercury at the 

 temperature of melting ice, 14.4521 grams in mass, of a 

 constant cross-sectional area, and of a length of io6>300 

 centimetres. 



To determine the resistance of a column of mercury in 

 terms of tlie international ohm, the procedure to be 

 followed shall be that set out in Specification .\ attached 

 to these resolutions. 



(6) The ampere is the second primary unit. 



(7) The international ampere is the unvarying electric 

 current which, when passed through a solution of nitrate 

 of silver in water, in accordance with the Specification H 

 attached to these resolutions, deposits silver at the rate 

 of o-ooiiiSoo of a gram per second. 



(8) The international volt is the electrical pressure 

 which, when stcadih' applied to a conductor whose resist- 

 ance is one international ohm, will produce a current 

 of one international ampere. 



(9) The international watt is the energy expended per 

 second by an unvarying electric current of one international 

 ampere under an electric pressure of one international voll. 



.\ comparison of these resolutions and those of the 

 Chicago Conference will show two main changes. 



In the first pl.ace there is no reference to the E.^LF. 

 of a standard cell in the definition of the volt, while in 

 the second the definitions of the international ohm, ampere, 

 and volt have been made more precise. As to the first 

 of these changes, after it had been decided that the volt 

 was to remain a derived unit, there was no difference of 

 opinion. The other, as a reference to the account of the 

 proceedings will show, gave rise to much discussion. The 

 increased precision, which it should be noted concerns the 

 definitions of ihe units, and probably does not affect the 

 concrete standards by which the units are expressed, is 

 arrived at in two wavs. In the first place, a distinction 

 is drawn between the ohm — 10^ C.G.S. units of resistance 

 — and the international ohm — the resistance of a definite 

 column of mercury. Previously, some such phrase as that 

 the ohm 10' C.G.S. units " is represented by the resist- 

 ance " of a certain column of mercury has been used ; 

 in the new resolutions it is stated that the international 

 ohm represents the ohm snffieienlly nearly for the purpose 

 of electrical measurements and as a basis for legislation, 

 and is the resistance of a certain column of mercury of 

 length 106-300 centimetres. Precision is given in the 

 second olace by the addition of the 00 after the 3 in the 

 above length, the internation.al ohm being thus defined 

 to one part in a hundred thousand. 



XO. 2035. VOL. 78] 



